1. Field of the Invention
The present invention relates to an electron emission device and an electron emission display, and more particularly, to an electron emission device having a grid electrode attached to a lower plate as an under gate structure, and an electron emission display having the same.
2. Discussion of Related Art
Generally, an electron emission device is classified as either a hot cathode type or a cold cathode type, wherein the hot cathode type and the cold cathode type respectively employ a hot cathode and a cold cathode as an electron emission source. A cold cathode type electron emission device includes a structure such as a field emitter array (FEA), a surface conduction emitter (SCE), a metal insulator metal (MIM), a metal insulator semiconductor (MIS), and a ballistic electron surface emitting (BSE).
The electron emission device having the FEA structure is based on the principle that a material having a low work function and a high β-function easily emits electrons due to an electric field difference as an electron emission source in a vacuum. Such an electron emission device having the FEA structure has been developed, which uses a tip structure, a carbon material, or a nano material as the electron emission source.
The electron emission device having the SCE structure includes an electron emitter, wherein a conductive layer is placed on a plate between two electrodes opposite each other and formed with a minute crack or gap, thereby forming the electron emitter. Such an electron emission device is based on the principle that the electron emitter formed by a minute crack or gap emits an electron when electric current due to a voltage applied between two electrodes flows through the surface of the conductive layer.
The electron emission device having an MIM or MIS structure includes an electron emission source having a metal-insulator-metal structure or a metal-insulator-semiconductor structure, and based on the principle that electrons are moved and accelerated from the metal or the semiconductor of high electric potential to the metal of low electric potential when a voltage is applied between the metal and the metal or between the metal and the semiconductor, respectively, thereby emitting the electrons.
The electron emission device having the BSE structure is based on the principle that when the size of a semiconductor is smaller than a mean free path of the electrons contained in the semiconductor electrons travel without sputtering. Such an electron emission device includes an electron supplying layer made of a metal or a semiconductor and formed on an ohmic electrode, an insulator formed on the electron supplying layer, and a thin metal layer formed on the insulator, so that electrons are emitted when voltage is applied between the ohmic electrode and the thin metal layer.
The foregoing electron emission devices are employed for an electron emission display, various backlights, and a lithography electron beam. Among these, the electron emission display includes an electron emission region provided with an electron emission device to emit electrons, and an image displaying region in which the emitted electrons collide with a fluorescent material to emit light. Generally, the electron emission display includes a plurality of electron emission devices formed on a first plate; a driving electrode to control the electron emission of the electron emission devices; a fluorescent layer formed on a second plate which collide with electrons emitted from the first plate; and a focusing electrode to effectively accelerate the electrons toward the fluorescent layer.
Further, in the case of an electron emission display having a triode structure of a cathode electrode, an anode electrode and a gate electrode, an electric field resulting from a predetermined voltage difference applied between the cathode electrode and the gate electrode causes the electron emitter to emit electrons and accelerates the electrons toward the fluorescent layer. Such an electron emission display has high brightness, similar to that of a cathode ray tube (CRT), and a wide view angle.
Referring now to FIG. 1, a conventional electron emission display having an under gate structure will be described. An electron emission display includes a rear plate 11 and a transparent front plate 12, which are opposite to and spaced apart at a predetermined distance by a spacer 13 placed in between. On the rear plate 11 a gate electrode 14 having a stripe pattern, a dielectric layer 15, and a cathode electrode 16 having a stripe pattern transverse to the gate electrode 14, are formed in sequence. Further, an electron emitter 17 is connected to the cathode electrode 16 and emits electrons. Between the cathode electrode 16 connected with the electron emitter 17 and the adjacent cathode electrode 18 is provided a counter electrode 19. The counter electrode 19 is connected to the gate electrode 14 through a hole formed in the dielectric layer 15. As such, the structure that the gate electrode 14 is disposed under the cathode electrode 16 and is called an “under gate structure”. On an inner surface of the transparent front plate 12 is formed an anode electrode 20. On the anode electrode 20 is discretely formed a fluorescent layer 21. Between the cathode electrode 16 and the anode electrode 20 is provided a grid electrode 22 for controlling the electrons emitted from the electron emitter 17 to be focused. The grid electrode 22 is supported by the spacer 13 at a predetermined position.
However, in the conventional electron emission display having the foregoing configuration, an annealing process is needed to connect the grid electrode 22, the spacer 13 and the transparent front plate 12 to one another. During the annealing process, the grid electrode 22 is likely to twist due to residual stress. Further, the grid electrode 22 is likely to sag due to its own weight. The twisting and sagging cause the electrons emitted from the electron emitter 17 to collide with the fluorescent layer not the at target area but at an adjacent area, thereby deteriorating color purity of the electron emission display. Therefore, high resolution is hard to achieve.